Hobson and McCarley's Theory of Dreaming (1977)
In 1977 two biologists Hobson and McCarley came up with the activation-synthesis model of dreaming that contested Sigmund Freud's (1900) theory of dreaming. It suggested that dreaming was for biological reasons, dreams were random and had no meaning. In this syllabus you are required to learn this biological theory of dreaming. Rundown '- How the brain sends signals' '- Activation synthesis' '- Sensory blockade, movement inhibition, REM sleep' '- Evaluation of activation synthesis theory' Parts of a neuron Neuron: A neuron is a cell in the nervous system that processes and sends information within the body, using chemical and electrical signals. The activity of neurons is central to how the brain and the body works. Neurons respond to stimulus in the environment. Axon: The ‘cable’ that leads from a cell body of a neuron down to the terminal buttons that hold the neurotransmitter. Passes messages away from the cell body to other neurons, muscles or glands. Impulse: The electrical signal that travels from the cell body of a neuron to the terminal buttons (down the axon), where it releases a neurotransmitter Dendrites: Receives messages from other cells Terminal branches: Form junctions with other cells Neurotransmitter: A chemical at the terminal button of a neuron, which is released by the impulse and then goes into the synaptic gap. Synaptic gap: The gap between the dendrites of one neuron and the next Synaptic transmission: What happens when a neurotransmitter released by an impulse of one neuron goes across the synaptic gap and is taken up at the dendrites of another neuron. How the brain sends signals Messages in the brain are sent using electrical impulses and chemicals that are called neurotransmitters. Step 1. An electrical impulse is triggered from the cell of one neuron then travels down the axon to the end. The impulse is also called action potential. Step 2. When the impulse gets to the end of the axon it releases a chemical, called a neurotransmitter, that is found in the terminal buttons at the end of the axon. Step 3. This neurotransmitter has to cross a gap, called the synapse or synaptic gap, to get to the dendrites of the next neuron to continue the message. Step 4. The neurotransmitter, released by the impulse, goes into the gap - where it could be taken up by the dendrites or could be lost. Step 5. If the receptors at the dendrites of the next neuron are ‘suitable’ to receive the neurotransmitter that is in the gap, then the chemical gets picked up. Step 6. The neurotransmitter sets off an electrical signal (by changing the chemical balance at the receptor) and then it drops back into the synaptic gap where it can be taken back up to be used again. Step 7. The receptors trigger an electrical impulse from the cell body, which then travels down to the end of the axon….return to step 1.(cycle) Lock and Key ''' Receptors at a dendrite will be a shape ‘lock’ to take up only a certain neurotransmitter ‘key’ and all other neurotransmitters will not be taken up. If someone takes drugs, the drug can fill the ‘lock’ of one neuron so that when a neurotransmitter message arrives in the gap, it cannot fit the receptor (which is already full). This means that the message is stopped or ‘blocked’. Pain killers can block messages of pain in this way. Activation Synthesis REM sleep is a stage of sleep where dreaming takes place. During REM sleep, any incoming information from the senses is blocked, this is known as sensory blockade. Physical movements are also blocked in REM sleep, this is known as movement inhibition. during REM no information is coming into the brain and no outgoing movements are made by the body. During REM sleep random neurons are activated because there are random impulses that give information as if it were coming from the senses. This is known as random activation and is the activation' part of the activation-synthesis theory. The brain then synthesizes the random thoughts and feelings into a story/sequence to make sense of it, making the synthesis part of the theory. '''REM sleep: A stage of sleep that occurs about 5 times each night, where rapid eye movement indicates that dreaming is taking place. Sensory blockade: During REM sleep no information is coming in through the senses Movement inhibition: During REM sleep the body is paralyzed and there is no movement Neurons: Neurons in the brain and how the messages are passed using electrical impulses down the axon and chemicals crossing the synapse Random activation: During REM sleep, neurons are still active - randomly not deliberately Evidence Evidence that Hobson and McCarley gave for their theory is that REM sleep happens regularly throughout a night's sleep, and happens regularly night after night. To test their theory they did brain scans on cats and found that the areas of the brain that were activated were responsible for movement inhibition and sensory blockade. By doing brain scans they provided evidence for sensory blockade and movement inhibition. Strengths - This theory was very objective, because the data used was quantitative and so could not be affected by the researcher's own opinions. - This theory was very reliable because they researchers used brain scans to measure brain activity. If the experiments were repeated the same results would be found. - This theory can explain why sometimes our dreams don't make sense - It was tested on cats for reliability Weaknesses - Dreams do have more meaning than activation-synthesis suggest, many people say they recognise parts of the dream from what has happened in their lives. - Activation synthesis suggests that dreams do not make sense, however studies have shown that only about 34% of 200 dreams do not make logical sense. Other studies also show that dreams often do make sense. - Lucid dreaming is when people are dreaming but know they are dreaming. Lucid dreaming has been tested and found to occur. It does not fit with activation-synthesis as it means dreams are controllable and not random. - Young children seem to have few dreams, yet they have a normal amount of REM sleep, suggesting that dreams may not be that linked to REM sleep Key Terminology # '''Neuron: '''a cell in the body that sends electrical and chemical messages # '''Axon: '''cell body of a neuron # '''Impulse: '''electrical signal # '''Neurotransmitter: '''chemical released by impulse # '''Synaptic gap: '''gap between the dendrites of one neuron and the next # '''Synaptic transmission: '''when a neurotransmitter crosses the synaptic gap # '''Activation synthesis model: '''model of dreaming that believes it is biological, dreams are random # '''Random activation: '''during REM sleep neurons are randomly activated # '''Sensory blockade: '''during REM sleep no information enters through the senses # '''Movement inhibition: '''during REM sleep the body is paralyzed